Both meters run at the same rate, which makes the crossover trivial to compute. The $32.85 monthly figure implies a 730-hour month: 0.045 x 730 = 32.85 [1][3][1]. Divide that back by the per-GB rate and you get 730 GB [2]. One terabyte through the gateway is 1024 GB, or $46.08, which already exceeds what the gateway costs to sit there doing nothing [2][3].
What the endpoint actually does is smaller than it sounds. Adding a gateway VPC endpoint puts a route in the subnet's route table, and traffic bound for S3 or DynamoDB takes a private AWS path instead of the default route out through NAT [8]. There is no device to size and no hourly rate: AWS's pricing page states that gateway-type endpoints carry no data-processing or hourly charges [7]. Those bytes leave the metered path rather than moving to a cheaper one.
The ceiling on that win is the destination mix. The traffic blamed for silent growth in the per-GB line includes package installs, container image pulls, telemetry shipped out and cross-region calls, and a gateway endpoint covers none of them [9]. The sequencing in the dev.to playbook concedes as much by putting measurement first: turn on VPC Flow Logs for the NAT'd subnets, look at where the bytes go, and treat a large share of S3 or DynamoDB destinations as the easy win [12]. Cost Explorer grouped by Usage Type splits NatGateway-Hours from NatGateway-Bytes, which separates arithmetic on gateway count from the number worth chasing [11]. On this evidence, S3 and DynamoDB are the only slices with a zero-cost exit; whether they are the largest slice is a per-account fact that Flow Logs settle and a pricing page cannot.
The AZ guidance is where the free advice runs out. AWS says keep resources in the same Availability Zone as the NAT Gateway, or run a gateway in each AZ that has resources, because otherwise traffic crosses the boundary to reach NAT and crosses back, paying inter-AZ transfer on top of processing [10]. Three AZs means three gateways: 3 x 32.85 = $98.55 a month in hours before a byte moves, $65.70 of it bought purely to avoid the boundary [4][5]. Whether that trades well depends on how many gigabytes cross, and the source quotes no inter-AZ transfer rate, so the breakeven is not computable from it.
Region matters more than the Ohio number suggests. In Sao Paulo both meters sit around $0.093 [6], which puts the fixed cost near $67.89 a month per gateway and every processed gigabyte at roughly 2.07 times the Ohio rate [6]. Partial hours bill as full hours, which matters to anyone standing up a VPC per branch [4]. And the processing charge is additive: standard AWS data transfer charges still apply on top [5].
Fifteen minutes in the console decides whether this is a $30 problem or a $3,000 one [14]. Until that runs, the endpoint change is free to make and unquantified in effect, and the line item stays named the same boring thing either way [15]. The rates above are as the dev.to writeup read AWS's VPC pricing and NAT Gateway docs in June 2026 [16].
